i) Field of the Invention
The present invention relates to a measurement probes for use with machine tools and the like and in particular to modular measurement probe apparatus.
ii) Description of Related Art
A variety of measurement probes are known. For example, touch trigger probes are known (e.g. see U.S. Pat. No. 4,153,998) that comprise a kinematic mechanism in which a stylus holder becomes unseated from an associated seat in the probe body when the stylus contacts an object. Unseating of the kinematic mechanism also breaks an electrical circuit allowing a “contact” or trigger signal to be generated. As an alternative to such tough trigger probes, it is also known to measure stylus deflection using strain gauges or the like and to either provide a measure of stylus deflection or to issue a trigger signal when a certain amount of stylus deflection has occurred.
Typically, for machine tools, the measurement probe is provided in the form of a single, mechanically robust, probe body in which the electronic circuitry and deflectable stylus mechanism are housed. The stylus is usually releasably attachable to the stylus holder mechanism of the probe body, for example by a screw thread, to allow different styli to be used for different measurement tasks and to allow worn or broken styli to be replaced. In a machine tool environment, it is typical to provide battery powered measurement probes that communicate with an associated probe interface over a wireless link. An example of such a wireless (RF) measurement probe is available from Renishaw plc under the product name RMP60. A modular version of the RMP60 measurement probe is also known in which various adaptors and extension bars allow a probe module to which a stylus can be attached to be located an extended distance from a probe body that houses the wireless (RF) communications and data processing electronics. Such a modular system is designed to improve the ability to measure inaccessible parts.